The present invention pertains to a device for gripping and holding a flat, preferably circular, disc-shaped substrate with a central opening, e.g., a compact disc. More particularly, the present invention relates to a device which comprises several grippers that are arranged in a housing, wherein the grippers are held and guided in recesses of the housing which allow a movement of the grippers transverse to the vertical axis of the housing. Magnets that cooperate with an electromagnet which is centrally arranged in the housing above the magnets are rigidly arranged on the ends of the respective grippers. The magnetic field axis of the electromagnet coincides with the vertical axis of the housing, and the electromagnet moves the grippers provided with magnets back and forward between two limiting stops depending on the polarity of the electromagnet.
The coating of circular substrates, e.g., glass or aluminum discs that serve as magnetic or magneto-optical data carriers, is known in the art from vacuum processing technology--in particular, thin-layer technology. These disc-shaped substrates are utilized as storage media for digital information. For example, embossed plastic discs are coated with an aluminum layer by means of a sputtering process. The sputtering systems used for this purpose usually contain an automated handling device for transporting the substrates in front, into and behind a vacuum chamber.
For example, a swivel arm of the handling system transports the substrates into the vacuum chamber from a cushion. In a typical chamber, the substrates are placed onto a rotary table, whereafter the substrates are transported to the individual stations of the vacuum chamber on this rotary table. Various devices for gripping and holding the substrates, i.e., for loading and unloading the rotary table, are known from the state of the art.
Until now, grippers that are actuated from outside the chamber by means of a linear motion leadthrough were most frequently utilized in vacuum chambers.
These known devices have the disadvantages that they usually contain an excessively high number of moving parts and that undesirable particles are produced due to the sliding motions in the linear motion leadthroughs. These particles are subsequently transported into the coating chamber and disadvantageously influence the result of the coating process. In addition, wear of the seals in such linear motion leadthroughs usually occurs after a certain time of operation. These worn seals always result in a leak in the vacuum chamber, i.e., time-consuming and expensive repairs need to be carried out.
A device for gripping and holding a flat, preferably disc-shaped substrate has already been proposed (G 93 07263.5). This device essentially consists of several finger-shaped grippers and a membrane of an elastic material which seals an opening arranged in a pressure-tight housing, wherein different pressures can be adjusted on the front side and the rear side of the membrane. The membrane is arranged in such a way that it carries out an excursion from its idle position if a differential pressure exists and returns into its idle position under the influence of a compression spring if the pressure on the front side and the rear side of the membrane is identical, and wherein one respective end of the grippers is mechanically connected to the membrane in such a way that their upper free ends carry out a swiveling motion that is proportional to the excursion of the membrane in order to grip and hold or release the substrate.
A device for gripping and holding a compact disc is also known (DE 195 29 945C2). This device consists of several finger-shaped grippers that are arranged in a housing in tiltable fashion, wherein the grippers are held and guided in openings in the top part of the housing which allow a tilting motion of the grippers about axes that extend transverse to the longitudinal axis of the housing. The tilting axes of all grippers extend in one plane and collectively form a polygon that encompasses the longitudinal axis. Magnets are rigidly arranged on the respective ends of the grippers which face away from the substrate, and the magnets cooperate with an electromagnet that is arranged in the housing above the gripper magnets. The magnetic field axis of the electromagnet coincides with the longitudinal axis of the housing. The electromagnet moves the gripper ends provided with magnets back and forward between two limit stops depending on the polarity of the electromagnet.
It is therefore an object of the present invention to make it possible to grip and hold substrates inside and outside of vacuum chambers in an extremely fast and particularly reliable fashion.
A further object of the present invention is to be able to compensate for slight irregularities and inaccuracies in the supply of the substrates so as to prevent damage to the sensitive substrates.